Process for making road surfaces



Patented Dec. 16, 1930 o UNITED STATES rATENTo-FFmE MARCEL LEVY, 0F GENEVAQSWITZERLAND, ASSIGNOR 0F ONE-HALF TO PRODORITE S. A., OF GENEVA, SWITZERLAND, ALCORPORATION OF SWITZERLAND rnoonss FOR MAKING ROAD SURFACES No Drawing. Application filed June 23, 1927, Serial No. 201,023, and in Germany July 2, 1926.

Great efforts have for a long time past been made to impartto road surfaces, more particularly in the case of macadamized roads, a surface which will prevent the for mation of dust, and will increase the resistance of the roadway to wear. For this purpose tar-like or bitumen-like substances have hitherto been employed in a liquid condition and have been poured either cold or warm it presents the disadvantage of forming surfaces which are not suficiently durable to meet the requirements of modern traffic.

In seeking for the cause of this failur-e,we have discovered a new, simple and cheap process, which produces road surfaces having much greater durability than those hitherto usual.

The process is based upon pouring on to the roadtar-like or bitumen-like substances, hot or cold, in a liquid condition or as an emulsion in the manner known in the case of surface tarring, sprinkling thereon stone or like powder which has been previously impregnated with bitumen or bitumen-like substances. If desired, some more or less broken stone may be scattered over the surface of the road after the same has been treated by the method of this application.

A stone powder impregnated with bitumen or any suitable stone powder, more particularly a limestone powder, which is impregnated with a bitumen-like or pitch-like substance, in the proportion varying from 10 to 15, or more, parts of bitumen or pitch to 100 parts of powdered stone, is used. The softening point of the bitumen or pitch may also vary widely. The selection of the softening temperature depends upon the nature or constitution of the tar employed for tarring the roadway, in such a way that by the mixing of this tar and of the impregnated stone powder a binding medium is obtained, which has the binding power necessary for the formation of a road surface, which in summer is not too soft, and in winter is not too hard. In this manner a road surface is obtalned,

which is far more durable than those surfaces which are made according to thetarring processes hitherto known.

Emample On to a macadamized or concrete road for example heated tar is poured in a known manner. Over the freshly tarred surface hot or cold stone powder previouslyimpregmated with bitumen is then scattered. This stone powder is of such fineness that it passes through a sieve of 800 meshes per square centimeter. Now this latter step is whatforms the characteristic feature of the new process according to my invention. The stone powder becomes saturated with tar and forms 1n a warm condition, or as an emulsion, provided that the liquid be enough fluid and heating the road surface be not necessary for allowing the liquid to penetrate therein.

The essence of the invention always resides in the fact that the coating of poured tar is'covered with stone powder previously impregnated with bitumen.

By the use of this powder thecoating of poured tar obtains an agglomerating power which it would never have if it were not covered with the powder impregnated with bitumen.

A road thus treated is completely impervious to water, whereby its durability is great- H M 1y increased.

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The road covering made according to this new process combines the advantage of the road coverings hitherto known, which are either tarred or provided with asphalt or petroleum residues, without exhibiting their disadvantages. The tar, or similar substances, which are poured on to the road at the beginning of the process penetrate below the surface and adhere firmly to the stones. They alone, however, do not suflice to give the covering the necessary strength, which is proved by the experiments hitherto made. The strength or durability is imparted solely by the stone powder impregnated with bitumen, which is sprinkled on immediately after the tarring, and mixed with the tar or tarlike substances. This substance accordingly imparts to the said stone powder the power of adhering firmly to the body of the road, which hitherto, as is known, has not been the case with asphalt roads, or with road coverings comprising tar or petroleum residues.

hat I claim is:

A process for improving a freshly tarred road surface consisting in scattering over the tarred surface a dry bituminous stone powder obtained by impregnating parts of powdered limestone with 10 to 15 parts of bitumen.

In testimony whereof I afiix my signature.

MARCEL LEVY. 

